Strain gauges are often used to measure forces, such as the deformation induced in a member by a load placed on the member, as a means of determining the weight of the load. A typical strain gauge transducer comprises the member (e.g., a cylindrical metal beam) and one or more strain gauges, which are configured as an electrical bridge circuit. The beam deforms as force is applied by a load. The bridge circuit has a plurality of arms, each of which includes an electrical resistor which is also deformed in conformity with the deformation of the beam.
The deformation of the resistors causes variations in resistance of one or more of the arms of the electrical bridge, effectively unbalancing it. Electronic circuitry measures the amount of the unbalancing of the bridge and determines therefrom the degree of deformation of the beam. From the information relating to the degree of deformation, and from the transducer's materials and design, the amount of strain being applied to the strain gauge--and hence the weight of the load--is determined.
The structure of the transducer is typically varied based on the particular application in which the strain gauge transducer is used. For example, in some strain gauge transducers, the beam is oriented vertically (i.e., in the same direction in which the load forces are applied). In others, the beam is oriented horizontally and is supported either in cantilevered fashion or at both ends.
In horizontal configurations, the electrical resistors that form the strain gauge are typically mounted to a so-called "shear-web" disposed in the interior of the beam. The shear-web is formed by cutting slots into the beam from both sides, leaving an elongated, flat vertical section of metal--the "web"--in the center of the beam (thus, in cross-section, the beam resembles an "I-beam"). The strain gauges are then attached to the web. The slots are either left open or covered with an electrical insulator, such as Teflon.